A: The short answer is, you can’t. There is no universal method of measuring flashlight output, not even when the ratings are in the same units. A lumen rating is the total unfocused visible light output of EITHER (depending on the manufacturer) the bare bulb, or of the entire flashlight. A candlepower rating used by a flashlight manufacturer will usually be Peak Beam Candlepower. This is a calculated value based on measuring the hot spot in the focused beam and multiplying by a number found by squaring the distance between the photocell used for the measurement and the flashlight. What this number gives is the number of “standard candles” that would need to be burning to produce the same amount of illumination as the hot spot in the beam at the same distance as the measurement is taken. Because Peak Beam Candlepower is focused light and lumens refer to unfocused light, it is ABSOLUTELY IMPOSSIBLE to convert the two.